Hedge Fun Is a Landscaping Firm That Specializes in Topiary

Hedge Fun is a landscaping firm that specializes in topiary.Last year,the firm had 60 employees and served 120 customers.This year,it had 70 employees and served 140 customers.The average product of labor is at a maximum when the number of customers is:

A) less than 120.
B) equal to 120.
C) between 120 and 140.
D) equal to 140.
E) greater than 140.